A comparison of the effectiveness of two strains of Rhizobium trifolii with trifoliumsubterraneum in agar and three soils

Abstract

Nitrogen fixation by two strains of Rhizobium trifolii was compared in a standard laboratory test and in two glasshouse tests using three soils of different acidity, available nitrogen, texture and natural R. trifolii content. In the soil tests, serological analysis showed that the inoculant strains produced a large proportion of the nodules. Heavy inoculation and the addition of mineral nitrogen before sowing both affected nodule formation, but had little effect on net nitrogen fixation. In the standard test, the ratio of nitrogen fixed by the two strains was 0.65:1, but was increased to 0.81:1 when 30 ppm nitrate-nitrogen was initially present. In the first soil test, conducted during the late autumn, the ratio of nitrogen fixed was 0.82:1 after 4–8 weeks' growth. In the second soil test, conducted during the spring, plant growth and nitrogen fixation were greater, strain differences were less consistent, and there was more strain × soil interaction in net nitrogen fixation.